Communication systems including electromagnetic transponders are more prevalent, particularly since the development of near-field communication (NFC) technologies.
Such systems use a radio frequency electromagnetic field generated by a device (terminal or reader) to communicate with another device (card).
In recent systems, a same NFC device may operate in card mode or in reader mode (for example, in the case of a near-field communication between two cellular phones). It is then frequent for devices to be powered with a battery and for their functions and circuits to be set to standby to avoid consuming power between periods of use. The devices then have to be “woken up” when they are within each other's range.